1. Field of the Invention
The present invention relates to a transcutaneous electric nerve stimulater for conducting a treatment on a stiffness, a paralysis, a pain, and the like by use of low-frequency signals.
2. Description of the Prior Art
In the prior art, there has been conducted a treatment in which a transcutaneous electric nerve stimulater is used to apply low-frequency pulses onto a human body so as to alleviate a stiffness, a paralysis, a pain, and the like of the body.
In order to effect an efficient treatment depending on a condition of the patient, such a transcutaneous electric nerve stimulater is provided with several operation modes. In one or more operation modes, the stimulater achieves an operation to repeatedly effect a sweeping operation of the frequency of the output pulses from a low frequency to a high frequency and an operation to change the frequency to a different discrete value, for example, form 1 Hz to 10 Hz. For this purpose, the transcutaneous electric nerve stimulater has a function to vary the frequency of the ouptut pulse.
In general, the function above is achieved such that a memory is disposed in the stimulater so as to beforehand store therein discrete values of frequency data such as 1 Hz, 10 Hz, 50 Hz, etc. According to a predetermined program, a frequency data item is read out form the memory so as to control an output level (high level or low level) to generate a pulse of a frequency corresponding to the data item, thereby changing the frequency of the output pulse. Incidentally, the method of changing the frequency of the output pulse by use of the frequency data stored in a memory is called a stored program control.
Incidentally, when a frequency of an output pulse applied to a human body is varied with a pulse width or amplitude kept unchanged, it has been known that a feeling of an electric shock on the human body generally decreases in a lower-frequency range and increases in a higher-frequency range.
This phenomenon also appears in the conventional transcutaneous electric nerve stimulater, which leads to a disadvantage that a uniform feeling of the electric shock is not obtained when the frequency of the output pulse is varied from a low frequency to a high frequency. In particular, when the frequency is discretely altered so as to jump from 1 Hz to 10 Hz, the electric shock on a human body greatly varies. In consequence, it is necessary to manually adjust the output level when the frequency is varied and hence there cnnot be attained a satisfactory practicability of the stimulater.
In addition, the transcutaneous electric nerve stimulater is provided in some cases with a function to invert a polarity of the output pulse inadition to the frequency change function. The polarity inverting function to invert the output pulse is included in a particular operation mode of the stimulater. The inversion of the output pulse is achieved in many cases at a point of time when the frequency of the output pulse is changed or at an arbitrary point (where a pulse to invert the polarity is to be outputted).
In the transcutaneous electric nerve stimulater of the prior art, when the frequency of the output pulse is varied or when the polarity thereof is reversed, an ouptut pulse is produced with a level identical to a level of the output pulse prior to the frequency change or the polarity inversion, which in consequence leads to a problem that the feeling of the electric shock is considerably increased.